apollo-link-http

title: apollo-link-http
description: Get GraphQL results over a network using HTTP fetch.

The http link is the most common Apollo Link, a system of modular components
for GraphQL networking. If you haven't done so already, read the Apollo Link
docs to learn about the Apollo
Link ecosystem and how to use this link with libraries like Apollo Client and
graphql-tools, or as a standalone client.

The http link is a terminating link that fetches GraphQL results from a GraphQL
endpoint over an http connection. The http link supports both POST and GET
requests with the ability change the http options on a per query basis. This
can be used for authentication, persisted queries, dynamic uris, and other
granular updates.

Usage

Import and initialize this link in just two lines:

import{createHttpLink}from"apollo-link-http";

constlink=createHttpLink({ uri:"/graphql"});

Options

HTTP Link takes an object with some options on it to customize the behavior of the link. If your server supports it, the HTTP link can also send over metadata about the request in the extensions field. To enable this, pass includeExtensions as true. The options you can pass are outlined below:

uri: the URI key is a string endpoint or function resolving to an endpoint -- will default to "/graphql" if not specified

includeExtensions: allow passing the extensions field to your graphql server, defaults to false

fetch: a fetch compatible API for making a request

headers: an object representing values to be sent as headers on the request

credentials: a string representing the credentials policy you want for the fetch call

fetchOptions: any overrides of the fetch options argument to pass to the fetch call

useGETForQueries: set to true to use the HTTP GET method for queries (but not for mutations)

Fetch polyfill

The HTTP Link relies on having fetch present in your runtime environment. If you are running on react-native, or modern browsers, this should be no problem. If you are targeting an environment without fetch such as older browsers or the server, you will need to pass your own fetch to the link through the options. We recommend unfetch for older browsers and node-fetch for running in Node.

Context

The Http Link uses the headers field on the context to allow passing headers to the HTTP request. It also supports the credentials field for defining credentials policy, uri for changing the endpoint dynamically, and fetchOptions to allow generic fetch overrides (i.e. method: "GET"). These options will override the same key if passed when creating the the link.

Note that if you set fetchOptions.method to GET, the http link will follow the standard GraphQL HTTP GET encoding: the query, variables, operation name, and extensions will be passed as query parameters rather than in the HTTP request body. If you want mutations to continue to be sent as non-idempotent POST requests, set the top-level useGETForQueries option to true instead of setting fetchOptions.method to GET.

This link also attaches the response from the fetch operation on the context as response so you can access it from within another link.

headers: an object representing values to be sent as headers on the request

credentials: a string representing the credentials policy you want for the fetch call

uri: a string of the endpoint you want to fetch from

fetchOptions: any overrides of the fetch options argument to pass to the fetch call

response: this is the raw response from the fetch request after it is made.

http: this is an object to control fine grained aspects of the http link itself, such as persisted queries (see below)

Persisted queries

The http link supports an advanced GraphQL feature called persisted queries. This allows you to not send the stringified query over the wire, but instead send some kind of identifier of the query. To support this you need to attach the id somewhere to the extensions field and pass the following options to the context:

Passing context per query

Apollo Client supports passing context separately for every query, so you can do things like pass a special header for a single query invocation if you need to.

importHttpLinkfrom"apollo-link-http";

importApolloClientfrom"apollo-client";

import{InMemoryCache}from"apollo-cache-inmemory";

constclient=newApolloClient({

link:newHttpLink({ uri:"/graphql"}),

cache:newInMemoryCache()

});

// a query with apollo-client

client.query({

query:MY_QUERY,

context:{

// example of setting the headers with context per operation

headers:{

special:"Special header value"

}

}

});

Errors

The Http Link draws a distinction between client, server and GraphQL errors. Server errors can occur in three different scenarios: parse, network and data errors. apollo-link-error provides an interface for handling these errors. This list describes the scenarios that cause different errors:

Client parse error: the request body is not-serializable due to circular references for example

Server parse error: the response from the server cannot be parsed (response.json())

Server network error: the response has a status of >= 300

Server data error: the parse request does not contain data or errors

GraphQL error: an objects in the errors array for a 200 level status

Since many server implementations can return a valid GraphQL result on a server network error, the thrown Error object contains the parsed server result. A server data error also receives the parsed result.

The table below provides a summary of error, Observable method called by the HTTP link, and type of error thrown for each failure:

Error

Callback

Error Type

Client Parse

error

ClientParseError

Server Parse

error

ServerParseError

Server Network

error

ServerError

Server Data

error

ServerError

GraphQL Error

next

Object

All error types inherit the name, message, and nullable stack properties from the generic javascript Error.

//type ClientParseError

{

parseError:Error;// Error returned from response.json()

};

//type ServerParseError

{

response: Response;// Object returned from fetch()

statusCode: number;// HTTP status code

bodyText: string // text that was returned from server

};

//type ServerError

{

result: Record<string, any>;// Parsed object from server response

response: Response;// Object returned from fetch()

statusCode: number;// HTTP status code

};

Custom fetching

You can use the fetch option when creating an http-link to do a lot of custom networking. This is useful if you want to modify the request based on the calculated headers or calculate the uri based on the operation:

Custom auth

constcustomFetch=(uri,options)=>{

const{header}=Hawk.client.header(

"http://example.com:8000/resource/1?b=1&a=2",

"POST",

{ credentials: credentials, ext:"some-app-data"}

);

options.headers.Authorization= header;

returnfetch(uri, options);

};

constlink=createHttpLink({ fetch: customFetch });

Dynamic URI

constcustomFetch=(uri,options)=>{

const{operationName}=JSON.parse(options.body);

returnfetch(`${uri}/graph/graphql?opname=${operationName}`, options);

};

constlink=createHttpLink({ fetch: customFetch });

Upgrade: Apollo Client 1.0

If you previously used either apollo-fetch or apollo-client's createNetworkInterface, you will need to change the way use and useAfter are implemented in your app. Both can be implemented by writing a custom link. It's important to note that regardless of whether you're adding middleware or afterware, your Http link will always be last in the chain since it's a terminating link.